Fluoropolymers are generally renowned for their chemical and physical inertness. Indeed, their excellent barrier properties and hydrophobic character are extensively exploited for applications such as moisture and noxious gas barriers, anti-corrosion and non-stick coatings. Examples of commonly used fluoropolymers include polytetrafluoroethylene, polyvinylidene difluoride, and copolymers of vinylidene difluoride with tetrafluoroethylene and hexafluoropropylene.
Multi-layer constructions containing fluoropolymers enjoy wide industrial application. Such constructions find utility, for example, in fuel line hoses and related containers and hoses or gaskets in the chemical processing field. Adhesion between the layers of a multi-layered article may need to meet various performance standards depending on the use of the finished article. However, in bonding applications between a fluoropolymer film and a non-fluorinated polymer film, the non-adhesive qualities of fluoropolymers can make it difficult to obtain a strong laminated bond.
Various approaches have been used to modify the surface of fluoropolymer substrates, including harsh chemical treatments such as alkali metal reduction (e.g., using alkali metal in liquid ammonia or sodium-naphthalene in glyme), and in the case of polyvinylidene difluoride, using concentrated alkali metal hydroxide solutions in the presence of a phase transfer catalyst. Other approaches include radiation treatments such as laser induced surface modification, and photoreduction of fluoropolymer substrates.
Each of the above processes has drawbacks. For example, alkali metal reduction requires maintenance of moisture-free conditions, the concentrated (8 N) alkali metal hydroxide process is relatively slow, and radiation induced processes require a radiation source that may be costly (e.g., a laser), and/or may not be well-suited to opaque substrates (e.g., photochemical reduction in the presence of electron donors).
It would be desirable to have new methods for chemically modifying fluoropolymers. It would also be useful to have new methods for chemically modifying surfaces of fluoropolymer substrates so that they can be bonded to non-fluorinated polymeric substrates, particularly if such methods are easily and quickly carried out and result in strong laminated bonds.